Organo-metallic aluminum catalysts for the preparation of polyesters



United States Patent ORGANO-METALLIC ALUMINUM CATALYSTS FOR THE PREPARATION or POLYESTERS John R- Ca d l; K ns pq t, Icons and Del ert D. Re

olds, Rochester, N. Y.,assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey i i No Drawing. Applicationoctohfil 1952,

Serial N0. 313,077

13 Claims. cram-7s This invention relates to a process for preparing polyesters which comprises condensing a diester of a dicarboxylic acid with a polyhydroxy compound in the presence of at least one of a, group of novel catalytic condensing agents ,which are alkali metal salts containing a complex aluminum tetraa lkoxide, radical and which are defined hereinbelow. These novel catalytic condensing agents can be advantageously employedin the preparation of linear polyesters wherein the dicarboxylic acid is an aromatic compound which does not contain any ethylenic (olefinie) unsaturation and the polyhydroxy compound is a dihydroxy compound. Inpreparing such linear polyesters it is advantageous to conduct the condensation in an inert atmosphere at an elevated temperature which is increased during the course of the condensation up to a temperature of from about2 25" to about 310 C., the condensation being conducted during the latter stages thereof at every ilow subatmospheric pressure.

This application contains subject matter disclosed to some extent in a .copending application, ,Serial No. 143,594, filed February 10, 11950, by J. R. Caldwell, now U. 8. Patent No. 2,614,120, dated October 14, 1 952. This application alsocontains subject matter disclosed in other copending applications ,filed on even dateherewith by I. R. Caldwell, Serial Nos. 313,061 through 313,071.

Various polyesters of dicarboxylic acids and polyhydroxy compounds are well known in the prior art and have been used, for ,example in the manufacture of paints and varnishes. Moreover, prior art disclosures set forth various linear condensation polyesters derived from .dihydroxy compounds and dibasic acids such as terephthalic acid which are capable of being drawnintofibers showing by characteristic X-ray patterns, orientation along the fiber axis. However, many of these lincar polyesters possess a relatively low melting point and a fairly considerable solubility in various solvents whereby they are of restricted utili y, especially in the textile field. These polyesters vary considerably in their characteristics, depending on the particular dicarboxylic acid and the particular polyhydroxy compound employed. Generally speaking, these polyesters have various physical characteristics which are not as satisfactory as could be desired.

The preparation of polyesters is well known in the prior art and involves the reaction of a dibasic dicarboxylic acid with a dihydric or polyhydric alcohol. It is advantageous to employ esters of the dicarboxylic acid whereby ester interchange takes place .with the .glycol or polyhydric alcohol to form a polyester and, an alcohol. When using the ester interchange method, the time required to form the gpolyesters is generally considerably less than when the free dicarboxylic acid is employed. The long chain in the polyester is built up by a series of ester interchange reactions wherein the glycol displaces a relatively low-boiling alcohol component of the acid ester to form a glycol ester. During the last stages of the reaction, it is generally desirable to heat .the condensing reaction mixturetoa temperature of about 225- ice 275 C. or higher in order to maintain the fluid state. For this reason, the properties of the catalytic condensing agent are very important.

A desirable catalytic condensing agent must be active enough to promote ester interchange :at a temperature below the boiling point of the glycol or other polyhydric alcohol. At the same time, the catalyst must be stable at temperatures of 225-310 C. or even higher if necessary. Furthermore, the catalyst must not cause decomposition or degradation of the polyester at these high temperatures.

In accordance with this invention, it has been found that certain compounds are especially valuable for use as catalytic condensing agents in the preparation of high melting linear polyesters. They have the general formula set forth below:

wherein M is an alkali metal, e. g. lithium, sodium, or potassium, and R is an alkyl radical containing from 1 to ,6 carbon atoms; R-can be derived from a lower aliphatic alcohol such as methyl, ethyl, propyl, n-butyl, isobutyl, n-amyl, etc.

These novel catalysts can be advantageouslyemployed in processes for preparing polyesters, which processes are described below. These novel catalysts are effective only when substantially anhydrous conditions are employed and no free acid is present to a sutliciently significant extent to destroy the catalyst compound; thus, when free acids are employed the acids are first reacted with a hydroxy compound (preferably the polyhydroxy compound to be employed in the polyesterification process) before the novel catalyst of this invention is added.

The novel bimetallic alkoxide catalysts can be made as described by Meerwein, Ann. 455, 227 (1927); 476, 113 (1929). Aluminum metal can be dissolved in an alcoholic solution of an alkali metal alkoxide whereby these novel catalysts are formed. Alternatively, a solution of aluminum alkoxide in alcohol or other inertsolvent can theoretically be mixed with an approximately equimolar quantity of an alkali metal alkoxide or solution containing-the same whereby these novel catalysts are formed; however, it is quite difficult to form a soluble aluminum alkoxide, hence this method is useful only .When extra precautions are taken to insure the formation of the desired novel catalyst. These novel catalysts can also be prepared by a process exemplified by reacting lithium aluminum hydride with ethyl or any of the other lower alcohols.

Care should be exercised .in preparing these novel catalysts to avoid the presence of insoluble aluminum alkoxide whichremains in the polyester being produced and has a deleterious effect on its properties when extruded or spun into fibers; see Example A. The ineffective use of the readily prepared insoluble variety of aluminum ethoxide is illustrated by Example B. This would seem to indicate that the aluminum ethoxide presentin Example A took no part in the condensation. Although the methoxide and ethoxide are employed in these examples, the same situation is applicable to the other lower alkoxides.

Example A.-Lithium methylate-aluminum ethylate catalyst A mixture of methyl terephthalate (200 g.) and ethylone glycol (200 g.) containing 5 cc. of lithium methylate, equivalent to 0.01 g. of lithium, and 0.25 g. of freshly prepared, finely divided aluminum ethylate (insoluble variety) was heated in an oil bath at 200 C. and in an atmosphere of nitrogen. The reaction mixture was then stirred and the excess glycol distilled under vacuum created by a water pump. After one-half hour a mechanical pump was attached to the system, and the stirring and heating (280290) continued for one hour at 0.5 mm. of Hg pressure. The resulting polymer was colorless, but the granular aluminum ethylate was present in the final products. This detracted greatly from the value of this polyester in extrusion, spinning and other methods of using it.

Example B.-Aluminum ethylate catalyst Two hundred grams of methyl'terephthalate, one hundred and thirty grams of ethylene glycol and 0.4 gram of aluminum ethylate (the easily prepared but alcohol insoluble variety) were heated in an atmosphere of nitrogen for 18 hours at 200 C. No appreciable reaction occurred during this time. When the reaction mixture cooled, the methyl terephthalate separated as the crystalline starting material.

' As shown by Meerwein, these catalysts are not merely mixtures of the two metallic alkoxides. They are definite compounds having a salt-like structure. The aluminum trialkoxide coordinates one mol of alcohol to form an acid having the structure:

This acid can then be reacted with a suitable alkali metal alkoxide e. g. sodium alkoxide, to give an acid salt having the structure:

These salts are much more effective as catalysts than either of the metal alkoxides used alone.

The novel catalysts of this invention give a very rapid reaction rate at all stages of the polyesterification process, including the final step where the molecular weight is built up. They are particularly valuable for the preparation of high melting polyesters from 1,6-hexanediol and 1,5-pentanediol, It is well known that these glycols have a tendency to decompose at temperatures above 250-260 C. and hence are diflicult to use. With the novel catalysts described above polyester reactions employing these glycols can be carried out at temperatures up to 300 C. or even higher without excessive decomposition.

The novel catalysts can, in general, be employed for the preparation of substantially all polyesters involving an ester interchange reaction between a dicarboxylic acid ester and a glycol or glycol ester. The catalysts are especially valuable for the preparation of polyesters that melt above about 240 C. as for example, polyethylene terephthalate. The process of the invention is applicable to all of the polyesters described herein.

By employing the novel catalysts of this invention, the reaction rate of the polyesterification process can be increased by a factor which is generally from about 2 to 5 times the reaction rate obtainable when catalysts known in the prior art are employed. Moreover, the novel catalysts of this invention have the valuable characteristic of minimizing side reactions which have the tendency of causing considerable degradation of the polyester products at the relatively high temperatures employed in preparing highly polymeric polyesters. Furthermore, by employing these novel catalysts to increase the rate of condensation, the time available for possible decomposition of The polyesters produced when employing these novel catalysts have greatly improved properties as compared to products obtained employing catalysts known in the prior art. The molecular weight is considerably higher whereby highly polymeric polyesters are obtained. The color of the polyesters obtained is excellent; the products 4 can therefore be employed for purposes calling for white or colorless materials. The physical properties of the polyesters obtained are also superior. At high temperatures there is a great improvement in the inherent viscosities of linear polyesters which are suitable for melt spinning or extrusion whereby fibers, films, etc. can be produced having properties superior to those obtainable with known catalysts.

The herein described novel catalysts are especially valuable for the preparation of polyesters employing diesters of p,p-sulfonyl dibenzoic acid as described in copending applications filed on even date herewith by J. R. Caldwell, Serial Nos. 313,061 through 313,068. Many of these polyesters are very high melting and the reaction must often be carried out at a temperature of 280- 300 C. or higher. It has been found that relatively few catalysts are effective at this temperature other than those described in this application.

It is an object of this invention to provide new and improved catalytic condensing agents for promoting the formation of improved polyesters in processes involving ester interchange and alcoholysis. A further object of this invention is to provide a new and improved method for the preparation of polyesters wherein such new and improved catalysts are employed. Other objects will become apparent elsewhere in this specification.

A broad aspect of this invention relates to a process for preparing a polyester which comprises condensing under substantially anhydrous conditions at an elevated temperature in an inert atmosphere a diester of a dicarboxylic acid with from about 1 to about 10 equivalent proportions of a polyhydroxy compound, in the presence of a catalytic condensing agent selected from the group consisting of those compounds having the formulas:

wherein M represents an alkali metal, and R represents an alkyl group containing from 1 to 6 carbon atoms.

More specifically, this invention relates to a process for preparing a polyester comprising (A) condensing under substantially anhydrous conditions an aromatic dicarboxylic acid diester having the formula:

wherein R1 and R4 each represents a substituent selected from the group consisting of an alkyl radical containing from 1 to 10 carbon atoms and an omega-hydroxyalkyl radical containing from 2 to 12 carbon atoms, R2 and R3 each represents (CH2)n-1 wherein n is a positive integer of from 1 to 5 inclusive and X represents a divalent aromatic radical selected from the group having the following formulas:

wherein Y represents a divalent radical selected from the group consisting of and the group consisting of those compounds having the following formulas:

and

wherein p represents a positive integeroffrom 2 to 12 inclusive, R5 and Rs each represents a .substituent selected from the group consisting of a hydrogen atom and an acyl radical containing trom2 to 4 carbon atoms, R: represents an alkylene radical containing from 2 to 4 carbon atoms and. q represents ,a positive integer of from 1 to inclusive, the alpha, omega-dioxy compound being employed in such .a proportion that there is at least an equivalent amount of alpha and omega oxy substituents in proportion to the carbalkoxysubstituents in the overall combination of the aromatic .diesters and the alpha, omega-dioxy compounds, (C) in the presence of a condensing agent selectedtrom the group consisting of the. novel catalysts set forth above, .(D). at; an elevated temperature which is increased gradually during the course of the condensation. up to a temperature of from about 225 to about 310 (3., (E) the condensation being conducted in an inert atmosphere,h(F) and, conducting the condensation at avery low pressure of the inert atmosphere during the latter part of the condensation.

, Advantageously, the condensing agent is employed in an amount of from about 0.005% toabout 0.2% based on the weight, of the aromatic dicarboxylic acid diester. Higher and lower. proportions can. also be employed.

Advantageously, the alpha, omega-.dioxy compound is employed in such ,a;propor.tion that there aret'rom about 1 .2 to about 3 alpha and omega oxy :substituents in pro portion to the car-balkoxy substituents in the overall combination of the aromatic diesters and-the alpha, omega dioxy compounds. Higher (e. g. IQ) and lower (c. g. 1) proportions can also be employed. t t t Since the alpha,.omega-dioxy compounds-which. can be employed in accordance with this invention are most advantageously alpha, omegardihydroxy compounds and in order to facilitate. thephraseology which is employed in this specification, such compounds will hereinafter be referred to as polyhydroxy or dihydrozgy' compounds although it is to be understood that the.;alpha,.omega-dioxy compoundssof the type described aboveare intended to be covered by. the termdihydroxy compoundsorthe term polyhydroxy compounds as such terms are ,employed herein.

Advanta eously, the temperature employed during the earlier part of the condensation- ;is from about 150 to about 220 C, Higher and lower temperatures can also, be employed. t

A ageo s y. t o Pr s u e ned u d r is less than about mm. ofl-Igpressure (preferablyless than 5 mm). However, somewhat higher pressures can also beemployed. H i

Most advantageously, the aromatic dicarboxylic acid; diester is a diester of p,p'sulf9nyl dibenzoic acid or terephthalic acid and the polyhydroxy, compound is. a polymethylene glycol.

This invention also includes processes as described above whereby polyesters can be prepared by replacing a part of the described aromatic dibasicacidqdicster with an ester of a replacement acid which can be an, aliphatic dibasic acid, e. g, carbonic; acid, oxalic acimsuccinic acid, dip acid, Sebacic acid, m imethylglutaric acid, di= methylmalonic acid, diglyeollic acid, a-oxyclipropionic acid, yaoxydibutyric'iacid,.ma1eici acid, fumaric acid, itaconic, iacid, etc. Similarly, other esterified acidic modifiers can, also be incorporated in conjunction with or in lieu of these replacement acid esters, e. g. linoleic acid, linolenic acid, fatty acids of linseed oil, soybean oil, cottonseed oil, tung oil, etc. The process described above for the general practice of this invention need not be appreciably modified when such partial replacement acid esters are employed in. conjunction with the aromatic dibasic acidesters except when they are unsaturated and tend to form insoluble and infusible productsdue to crosslinkage effects, in which event; the process described here inabove is advantageously terminated at an intermediate temperature of about 250 .-C before the pressure is reduced whereby products areobtained which can be called soluble intermediate polyesters which are useful in pre paring protective coatings. The various polyesters containing replacement acid esters as described in this paragraph can be prepared according to procedures similar to thoserdescribed in copending applications filed on even date herewith by I. R, Galdwell, Serial Nos. 313,062 through 313,066.

Polyesters. can also be prepared. in accordance with this invention by replacing a part of the described dihydroxy compound with what can be called a polyhydroxy compound (which contains 3 or more hydroxy radicals, e. g. glycerol, sorbitol, pentaerythritol, dipentaerythritol, firmethylglycerol, 2-.methyl-2-hydroxymethyl-1,3-propanediol, 1,2,4-trihydroxybutane, etc, In the. preparation of polyesters employing these polyhydroxy compounds, the reaction. mixture isanot generally heated to the high temperatures under reduced pressure as described hereinabove since the product would become insoluble and infusible due to cross-linking of the molecules; hence, the process is halted at about 250 C. or less prior to the reduction in pressure of the inert atmosphere. Various solutions can then be prepared from these soluble polyester products which can then be cast into films or otherwise used in protective coating compositions. In preparing such soluble polyesters it is generally advantageous to employ an unsaturated aliphatic dibasic acid diester in lieu of a part of the described aromatic .dibasic acid diesters, e. g. maleic, fumaric and itaconic diesters. The various polyesters containing replacement polyhydroxy compounds as described in this paragraph canbe prepared according to procedures similar to those described in a copending application filed on even date herewith by J. R. Caldwell, Serial No. 313,069.

The dihydroxy or polyhydroxy compounds defined above may not actually contain any free hydroxy radicals since they may be in. esterified form .as indicated by the formulas of the dihydroxy compounds set forth above. However, these hydroxy or substituted hydroxy radicals are referred to. generally as hydroxy radicals or substituents. Each diester is considered as containing two carbalkoxy radicals as that term is. employed in the definition of the process as described above since R1 and R4. may be alkyl radicals, or omega-hydroxyalkyl radicals. Even when the process is preceded by the preliminary step described below employing free acids, the term carbalkoxy radicals in the description of the process is intended to encompass such free carboxy radicals.

Furthermore, this invention covers processes as defined above wherein the aromatic dicarboxylic acid diester is formed by a preliminary step comprising condensing an aromatic dicarboxylic acid having the formula:

(wherein R2, R3 and X are defined under (A) in the above-described process), with a polyhydroxy compound which is defined above under (B) and is employed in the proportions set forth under (B), at an elevated temperature, after which preliminary step the novel catalytic condensing agent which is defined under (C) is added and the condensation is completed as defined under (D), ('E) and(F). Advantageous'ly, the elevatedtemperature employed during the preliminary step is substantially that at which reflux conditions subsist; however, higher and lower temperatures can also be used. Advantageously, as indicated hereinbefore, the polyhydroxy compound is employed in such a proportion that there are from about 1.2 to about 3 hydroxy substituents in proportionto the acid substituents in the overall combination of the aromatic diester and'the polyhydroxy compound. 7

In preparing polyesters, especially linear highly polymeric polyesters, it is important to exclude oxygen and moisture at all stages of the condensation, particularly during the latter stages thereof. An inert atmosphere is employed to exclude oxygen; such atmospheres include helium, hydrogen, nitrogen, etc. The reacting materials employed in the condensation are advantageously substantially anhydrous; however, if water is initially present or is formed during the course of the condensation, it can be substantially completely removed prior to the final stages of'the condensation by operating in accordance withthe specified process or otherwise.

Examples of aromatic dicarboxylic acid diesters which can be employed as defined above under (A) include the ,s-hydroxyethyl diester of p,p'-sulfonyl dibenzoic acid, p,p'-sulfonyl dibenzoic acid dibutyl ester, m,p'-sulfonyl dibenzoic acid dipropyl ester, m,m-sulfonyl dibenzoic acid dihexyl ester, methyl terephthalate, hexyl terephthalate, isopropyl terephthalate, as well as various esters having the following formulas:

oo an.

03 959 I torm -s -o0-0 on;

o1H5oo O-QO- cHm-OO-C 0-0 02115 onto-o c-OsGs-O-o o-o CH3 ([3211: V 021150-00 N -COOC2H5 et cetera.

The dihydroxy compounds which can be employed to form highly polymeric linear polyesters are straight-chain alkane diols, viz. polymethylene glycols, wherein the hydroxy radicals are positioned at the two ends of the alkylene chain. Examples of such glycols include ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6- hexylene glycol, 1,10-decamethylene glycol, 1,12-dodecamethylene glycol, etc. As indicated above, mono or diesters of these glycols can also be employed. Thus, the acetates, propionates and butyrates are examples of such esters. The defined ether glycols can be employed either in lieu of the polymethylene glycols or in conjunction therewith as modifiers. Examples of ether glycols include diethylene glycol, triethylene glycol, tetraethylene glycol, bis (4-hydroxybutyl) ether, bis (3-hydroxypropyl) ether, etc.

Valuable fibers can be advantageously prepared employing the higher melting polyesters which can be produced according to the procedures described herein. Preferably no aliphatic ether glycol is employed when fibers are to be prepared. Furthermore, the aromatic acid diesters should ordinarily contain only p,p linkages when highly polymeric linear polyesters are desired. However, on the other hand, valuable polyesters can be prepared employing aliphatic ether glycols without any polymethylene glycol although the product obtained will not-be suitable for forming useful fibers. The same applies to' the employment of aromatic diesters containing linkages in other than the para positions.

The catalytic condensing agents which can be employed have been described above. From about'0.005 to about 0.2% of such catalysts based on the weight of the diesters being condensed can be employed. Higher or lower percentages can also be employed. Generally, from about 0.01% to about 0.06% of the catalytic condensing agent can be advantageously employed based on the weight of the various diesters being condensed. The temperature at which polyesterification can be conducted is dependent upon the specific reactants involved in any given reaction. In general, the reaction mixture can be heated with agitation at from about 150 to about 220 C. for from approximately one to three hours in an inert atmosphere (e. g. nitrogen or hydrogen); the mixture can then be heated with agitation at from about 225240 to about 280310 C. in the same atmosphere for approximately 1 to 2 hours. Finally, the pressure can be greatly reduced to form a vacuum (less than about mm. of Hg pressure but preferably on the order of less than 5 mm. of Hg pres sure) while the temperature is maintained in the same range (225 3 10 C.); these conditions are advantageously maintained for approximately 1 to 6 additional hours. Thisfinal phase is advantageously carried out with good agitation under the high vacuum in order to facilitate the escape of volatile products from the highly viscous melt. The conditions can be varied considerably depending upon the degree of polyesterification desired, the ultimate properties sought, the stability of the polyester being produced, and the use for which the product is intended.

-The reaction can be carried out in the presence or absence of a solvent. Inert, high boiling compounds, such as diphenyl ether, diphenyl, mixed tolyl sulfones, chlorinated naphthalene, chlorinated diphenyl, dimethyl sulfolane, etc., can be used as the reaction medium.

75 In the examples given below, the hot bar sticking temperature is referred to in several instances. The hotbar sticking test can be briefly described as follows: A polyester fiber is placed on the flat surface of a heated bar and aweight of 100 grams is applied to the fiber along a distance of /8 inch of the fiber length. The contact surface of this weight has a coating of polytetrafluoroethylene which acts as a thermal insulator. The fiber is allowed to remain in contact with the bar under this weight for one minute. The minimum temperature at which the fiber adheres to the hot bar under these conditions is the sticking temperature as that term is employed in the examples given herein.

This invention can be further illustrated by the following examples; in addition to these examples it is apparent that other variations and modifications thereof can be adapted to obtain similar results:

Example 1.-Li(Al(OC2H5)4) as the catalyst A mixture of 200 g. methyl terephthalate, 130 g. ethylene glycol and 5 cc. of catalyst, prepared by dissolving one gram of lithium aluminum hydride in 100 cc. of absolute ethanol, was heated under nitrogen at 220-270 for one and one-half hours; Ethanol was distilledoff through a 10" Vigreux column. A stirrerand water pump were then attached to the system, andglycol was distilled from the reaction mixture at 290-300 for fifteen minutes, and then a mechanical pump was attached. The reaction was continued for one hour and fifty minutes under a very high vacuum. A clear product was obtained which crystallized rapidly as it cooled. It had an intrinsic viscosity of 0.90 in a 60:40 s-tetrachloroethane: phenol mixture.

Example 2.-Li(Al(OC2H5)4) as the catalyst A mixture of 110 g. of dibutyl ester of p,p'-sulfonyl dibenzoicacid, 110 g. 1,5-pentanediol and 5 cc. catalyst prepared as described in Example 1 was heated at 200- 270 for one and one half hours. Butanol distilled off. Excess glycol was then distilled under a water-pump vacuum. A stirrer was attached, and the reaction continued. at 290 at 1 mm. of Hg pressure. Within fifteen minutes a clear, colorless polymer had become wrapped around the stirrer shaft. it has an intrinsic viscosity of 0.70. r r

Example 3.-Na(Al(OC4H9)4) as the catalyst Eighty-four g. [0.2 mol] of p,p-sulfonyl dibenzoic acid butyl ester and 36 g. [0.3 mol] of l,6-hexanediol' were placed in a vessel equipped with a variable speed anchor stirrer, a short distillation column and a gas inlet tube for the entrance of purified hydrogen. Two cc. ofQnbutyl alcohol containing 0.1 g. sodium aluminum butoxide was added. The mixture was heated in a metal bath at ZOO-210 C. and stirred at 100-120 R. P. M. while pure hydrogen was passed over the surface. Butyl alcohol distilled off rapid and the ester interchange was practically complete in 40 minutes. The temperature was then raised to 280-285 C. in minutes and heating continued for 10-15 minutes. Some of the excess glycol distilledoif during this stage. The hydrogen gas was shut olf, and a vacuum of about 1 mm. was applied. The melt rapidly increased in viscosity and in about 15 minutes it was necessary to reduce the stirrer speed to 40 R. P. M. As the viscosity increased, the stirrer speed was gradually reduced; After a total time of 30-40 minutes undervacw urn, the melt had become too viscous to stir and the 1133C? tion was stopped. The melt was clear and colorless. After cooling slowly, the product obtained was hard and opaque, due to crystallinity. cooled or quenched, it has a tendency to remain amorphous and transparent. On a hot stage, in polarized light, the crystalline material shows a melting point of 27 0-2 80? .C. The inherent viscosity in 60% phenol-40% tetrachlorethane is 0.70-0.80. Fibers can be pulled from the melt and cold-drawn 500-600 per cent. They stick If the melt is suddenly 10 one hQt'barat 23.0-24.0 .C. The polyester also gives valuablesheetsand'films,

Example 4;.-K(Al(OC2H5)4) as the catalyst Onehundred g. p,p.- sulfonyl dibenzoic acid ethyl ester and 40 g. 1,5-pentanediol wereplaced in a reaction vessel equipped with a stirrer, a short distillation column, and an inlet tube for purified nitrogen. Five cc. of ethyl alcohol containing 0.4 g. potassium aluminum ethylate was added andthe mixture was heatedat 180-200" C. with stirring. After 1 hour, the distillation of ethyl alcohol ceased, and the temperature was raised to 280-285 C. where it was held for 20 minutes. A. vacuum of 0.5 to 1.0 mm. was applied for 1 hour, while the temperature was maintained at 280-285 C. A colorless product having an inherent viscosity of 0.80-0.90 in 60% phenol-40% tetrachloethane solution was obtained. Fibers pulled from the melt and cold drawn 400-500 per cent show a sticking temperature of 240-250 C. The product is also useful for films and sheets.

Example 5 .-Na (Al(OC2 Hs) 1) as the catalyst One gram mol of methyl sebacate, 4 gram mols of p,p'- sulfonyl dibenzoic acid, butyl ester, and 7 gram mols 1,6- hexanediol were placed in a vessel. as described in- Example 4. Five-hundredths per cent sodium aluminum ethoxide was added, based on the weight of the two esters. A heating schedule similar to that given in Example 4 was followed. The product obtained, is very tough and rubbery. It has an inherent viscosity of 0.80 in a solvent of 60% phenol-40% tetrachlorethane. Fibers pulled from the melt show a rubbery elastic elongation of 30-40 per cent. This product is also useful as a molding plastic.

Example 6.K(Al(O-iso-C4H9)4) as the catalyst Example7.-Na(Al(OCzH5)4) as the catalyst One hundred g. methyl terephthalate and 40 g. ethylene glycol were placed in a vessel as described in Example 3. Three-hundredths per cent sodium aluminum ethoxide wasladded, based on the weight of methyl terephthalate. A heating schedule was followed as described in Example 3. A polyester having excellent color and an inherent viscosity of 0.80-0.90 was obtained.

Example 8.-Na (Al(OC2H5)4) as the catalyst Three hundred and seventy-two grams (1.0 mol) of p,p-sulfonyldibenzoic acid diethyl ester, g. (0.5 mole) dimethylmalonicacid diethyl ester, and 300 g. pentamethylene glycol were placed in a reaction vessel as described in Example; 3. A solution of 0.2 g. sodium aluminum ethoxide in ethyl'alcohol was added as catalyst. The mix ture was heated and stirred at 200-210" C. in a stream of pure nitrogen for'2 hours to remove ethyl alcohol. The

temperature was then raised to 250 C. and held for 30 minutes. A vacuum of 2.0 to 3.0 mm. was applied for 2 hours. The product obtained has a softening point of about 200. C. After it has been oriented and heat treated; it sticks to the hot bar at 180-190 C. Thispolyester can be molded and extruded to give products that.

show good impact properties. It is useful as a photographic film base and as electricalinsulation.

Example 9.K(AI(OC2H 5)4) as the catalyst Three hundred and seventy-two g. (11.0 mol) p,p'- sulfonyldibenzoic acidadiethyl ester, 106 g. (1.0 mol) diethylene glycol, and 72 g. (0.8 mol) tetramethylene glycol were placed in a reaction vessel as described in Example 3. A solution of 0.3 g. potassium aluminum ethoxide in ethyl alcohol was added as catalyst. The mixture was heated according to the schedule described in Example 8 using a final temperature of 270-275. The product obtained has an inherent viscosity of 0.80 in 60% phenol-40% tetrachlorethane. This polyester is especially valuable as a source of fibers. When melt spun and drafted, it gives fibers having a tensile strength of 3 to 4 grams per denier and 1825% elongation. They have excellent elasticity and can be dyed readily with cellulose acetate dyes. The fibers stick on the hot bar at 220-230 C.

Example I0.Na(Al(OC2H5)4) as the, catalyst Four hundred and twenty g. (1.0 mol) of p,p'-sulfonyldibenzoic acid dibutyl ester, 50 g. (0.25 mol) dimethyl orthophthalate, and 250 g. pentamethylene glycol were reacted, using 0.25 g. sodium aluminum ethoxide catalyst according to the process and using the apparatus described in Example 9 except for the change of the catalyst. The product is especially valuable as a molding plastic, electrical insulator, and photographic film base. It shows excellent extrusion properties. When oriented and heat treated, films of the polyester have a hot bar sticking temperature of 170180 C.

Example I1.--Li(Al(OC2I-I5)4) as the Four hundred and twenty g. (1.0 mol) of p,p-sulfonyldibenzoic acid dibutyl ester, 194 g. (1.0 mol) dimethyl orthophthalate, and 300 g. tetramethylene glycol were placed in a reaction vessel as described in Example 3. A solution of 0.3 g. lithium aluminum ethoxide in cc. ethyl alcohol was added as catalyst. The mixture was heated at 200-210 C. until the distillation of butyl and methyl alcohols was practically complete. The temperature was then raised to 255-260 and held for 45 minutes. A vacuum of 1 to 2 mm. was applied and stirring continued for 1.5 to 2 hours. The product obtained has an inherent viscosity of 0.7 to 0.8 in 60% phenol-40% tetrachlorethane. This polyester is especially valuable as a molding plastic because it has a relatively wide softening range and shows good flow properties during extrusion. It is also useful as a photographic film base. When oriented by drafting and then heat treated, fibers and films show a hot bar sticking temperature of 190200 C.

5 Example 12.-Na(A1(OC2H5)4) as the catalyst One hundred and forty-six grams (1.0 mole) of ethyl oxalate and 212 g. (2.0 moles) of pentamethylene glycol were heated in a flask equipped with a fractionating column. Sodium aluminum cthoxide (0.3 g.) was used as catalyst. After approximately 1.8 moles of alcohol had been distilled off, the product was transferred to a reaction vessel equipped with a stirrer, a short distillation column, and an inlet for purified nitrogen. The product obtained was essentially a low molecular weight pentamethylene oxalate polyester. Seven hundred and fortyfour grams (2.0 moles) of p,p-sulfonyldibenzoic acid and 300 g. of pentamethylene glycol were added to the reaction vessel. The mixture was stirred at 200-210" C. in a stream of purified nitrogen. The evolution of ethyl alcohol practically stopped after 2 hours. The temperature was raised to 260 C. and held for 30 minutes. A vacuum of 1.0 to 2.0 mm. was applied and stirring continued for 2 to 3 hours. The product obtained has an inherent viscosity of 0.5 to 0.6 in 60% phenol-40% tetrachlorethane. The polyester can be molded by incatalyst jection methods. It can be extruded to make films, tubes,

rods, etc. The product can be melt-spun to give filaments that melt at ZOO-210 C. after they have been drafted.

Example 13.Na(Al(OC2H5)4) as the catalyst Three hundred and seventy-two grams (1.0, mol) p,p'-

sulfonyl dibenzoic acid diethyl ester, g. (1.0 mol) diethyl succinate, and 400 g. pentanediol-l,5 were placed in a reaction vessel as described in Example 3. Ten cc. of ethyl alcohol containing 0.40 g. sodium aluminum ethoxide was added as catalyst. The mixture was heated and stirred at 200-210 in an atmosphere of purified hydrogen. Ethyl alcohol distilled off rapidly from the reaction mixture and the ester interchange was practically complete in 2 hours. The temperature was then raised to 25 0260 C. Where it was held for one hour. A vacuum of l to 2 mm. was applied and the melt stirred at 250- 260 for 3 to 3.5 hours. The product obtained has an inherent viscosity of 0.8 to 0.9 in 60% phenol-40% tetrachlorethane solution. The polyester can be extruded as film, rods, tubes, or sheets. It can be injection molded to give products that retain their shape up to l60l80 C. Fibers can be spun by the usual melt-spinning methods.

Example 1 4 .-Na (Al( OCzHs) 4) as the catalyst Three hundred and seventy-two grams (1.0 mole) of p,p-sulfonyldibenzoic acid diethyl ester, 47 g. (0.25 mole) diglycollic acid diethyl ester, and 500 g. pentamethylene glycol were placed in a reaction vessel equipped with a stirrer, short distillation column, and an inlet for purified nitrogen. A solution of 0.2 g. sodium aluminum ethoxide in ethanol was added as catalyst. The mixture was stirred at 200-2l0 C. until the distillation of ethyl alcohol was essentially complete. The temperature was then raised to 250260 C. and maintained for 30 minutes; A vacuum of 2 to 3 mm. was applied and stirring continued for 3 hours. A product having an inherent viscosity of 0.7 to 0.8 in 60% phenol-40% tetrachlorethane was obtained. The polyester is useful as a molding plastic. It can be extruded at 200220 C. to give sheets, rods, tubes, etc. It is useful as a photographic film base material.

Example 15.Na(Al(OC4H9)4) as the catalyst One gram mole of p,p'-sulfonyldibenzoic acid, 1.5 gram moles octamethylene glycol, and 0.5 mole ethylene glycol were reacted according to the procedure using the apparatus described in Example 3 and employing sodium aluminum butoxide catalyst to give a product softening at ZOO-220.

Example 1 6 .K(Al( OC2H5 4) as the catalyst One gram mole of p,p'-dicarbethoxydiphenyl methane and 2.1 gram moles of ethylene glycol were condensed in apparatus as described in Example 4 according to the procedure set forth therein employing 5 cc. of the same catalyst solution. The product obtained was a highly polymeric linear polyester useful as a molding resin, for preparing films, sheets, etc.

Example 17.K(Al(OC2H5)4) as the catalyst One gram mole of p,p'-dicarbomethoxybenzophenone and 2.4 gram moles of trimethylene glycol were condensed in apparatus as described in Example 4 according to the procedure set forth therein employing 5 cc. of the same catalyst solution. The product obtained was a highly polymeric linear polyester useful as a molding resin, for preparing films, sheets, etc.

Example 18.K(Al(OC2H5)4) as the catalyst One gram mole of 1,2-bis(p-carbopropoxyphenyloxy) ethane and 2.5 gram moles of ethylene glycol were condensed in apparatus as described in Example 4 according to the procedure set forth therein employing 5 cc. of the same catalyst solution. The product obtained has a highly polymeric linear polyester useful as a molding resin, for preparing films, sheets, etc.

Polyesters similar to those described in the above examples can be prepared employing 1,4-bis(p-carbamyloxyphenoxy) benzene, bis(p-carbethoxyphenyl) sulfide and N,N-bis(p-carbohexoxyphenyl) methylamine, condensed 13 with ethylene glycol, tetramethylene glycol and hexamethylene glycol.

In the various formulas given for the catalysts in the above examples, C4H9 and the formulas for other such alkyl radicals are intended to represent the straight chain alkyl radicals. However, branched chain radicals can also be employed, e. g. see Example 6.

We claim:

1. A process for preparing a polyester comprising (A) condensing under substantially anhydrous conditions an aromatic dicarboxylic acid diester having the formula:

wherein R1 and R4 each represents a substituent selected from the group consisting of an alkyl radical containing from 1 to 10 carbon atoms and an omega-hydroxyalkyl radical containing from 2 to 12 carbon atoms, R2 and Rs each represents (CH2)n-l wherein n is a positive integer of from 1 to inclusive, and X represents a divalent aromatic radical selected from the group consisting of those having the following formulas:

and

wherein Y represents a divalent radical selected from the group consisting of and wherein m is a positive integer of from 1 to 5 inclusive, (B) with an alpha, omega-dioxy compound comprising a compound selected from the group consisting of those compounds having the following formulas:

wherein p represents a positive integer of from 2 to 12 inclusive, R5 and Re each represents a substituent selected from the group consisting of a hydrogen atom and an acyl radical containing from to 4 carbon atoms, R1 represents an alkylene radical containing from 2 to 4 carbon atoms and q represents a positive integer of from 1 to inclusive, the alpha, omega-dioxy compound being employed in such a proportion that there is at least an equivalent amount of alpha and omega oxy substituents in proportion to the carbalkoxy substituents in the overall combination of the aromatic diester and the alpha, omega-dioxy compound, (C) in the presence of a catalytic condensing agent selected from the group consisting of compounds having the following formula:

M(Al(OR)4) wherein M represents an alkali metal and R represents an alkyl radical containing from 1 to 6 carbon atoms, (D) at an elevated temperature which is increased gradually during the course of the condensation up to a temperature of 14 from about 225 to about 310 C., (E) the condensation being conducted in an inert atmosphere, (F) and conducting the condensation at a very low pressure of the inert atmosphere during the latter part of the condensation.

2. A process as defined in claim 1 wherein the condensing agent is employed in an amount of from about 0.005% to about 0.2% based on the weight of the aromatic dicarboxylic acid diester.

3. A process as defined in claim 2 wherein the alpha, omega-dioxy compound is employed in such a proportion that there are from about 1.2 to about 3 alpha and omega oxy substituents in proportion to the carbalkoXy substituents in the overall combination of the aromatic diester and the alpha,omega-dioxy compound.

4. A process as defined in claim 3 wherein the elevated temperature employed during the earlier part of the condensation is from about C. to about 220 C.

5. A process as defined in claim 4 wherein the low pressure defined under (F) is less than 15 mm. of Hg pressure.

6. A process as defined in claim 5 wherein the low pressure defined under (F) is less than 5 mm. of Hg pressure.

7. A process as defined in claim 6 wherein the aromatic diester is derived from p,p'-sulfonyl dibenzoic acid and the condensing agent is sodium aluminum tetrabutoxide.

8. A process as defined in claim 6 wherein the aromatic diester is derived from p,p-sulfonyl dibenzoic acid and the condensing agent is potassium aluminum tetraethoxide.

9. A process as defined in claim 6 wherein the aromatic diester is derived from p,p'-sulfonyl dibenzoic acid and the condensing agent is lithium aluminum tetraethoxide.

10. A process as defined in claim 6 wherein the aromatic diester is derived from terephthalic acid and the condensing agent is lithium aluminum tetraethoxide.

11. A process as defined in claim 6 wherein the aromatic diester is derived from terephthalic acid and the condensing agent is potassium aluminum tetraisobutoxide.

12. A process as defined in claim 1 wherein the aromatic dicarboxylic acid diester is formed by a preliminary step comprising condensing an aromatic dicarboxylic acid having the formula:

wherein R2, R3 and X are defined under (A), with an alpha,omega-dioxy compound which is defined under (B) and is employed in the proportions set forth under (B), at an elevated temperature, after which preliminary step the catalytic condensing agent which is defined under (C) is added and the condensation is completed as defined under (D), (E) and (F).

13. A process as defined in claim 12 wherein the elevated temperature employed during the preliminary step is substantially that at which reflux conditions subsist, and the condensing agent is employed in an amount of from about 0.005% to about 0.2% based on the weight of the aromatic dicarboxylic acid diester, the alpha, omega-dioxy compound is employed in such a proportion that there are from about 1.2 to about 3 alpha and omega oXy substituents in proportion to the acid substituents in the overall combination of the aromatic diester and the alpha,omega-dioxy compound, the elevated temperature employed during the earlier part of the condensation to form the polyester is from about 150 C. to about 220 C., the low pressure defined under (F) is less than about 15 mm. of Hg pressure and all materials employed in the process are substantially anhydrous.

References Cited in the file of this patent UNITED STATES PATENTS 2,512,410 Adelson et a1 June 20, 1950 OTHER REFERENCES Meerwein Ann. 455, 227 (1927); 476, 113-150; 1929). 

1. A PROCESS FOR PREPARING A POLYESTER COMPRISING (A) CONDENSING UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS AN AROMATIC DICARBOXYLIC ACID DIESTER HAVING THE FORMULA: 